1. Field of the Invention
The present invention relates to a semiconductor Hall element. More particularly, the present invention relates to a vertical Hall element configured such that current containing a component perpendicular to a surface of a semiconductor substrate is supplied to a magnetic sensing portion in the semiconductor substrate and a magnetic field component in parallel with a surface of the semiconductor substrate is detected through Hall voltage generated in relation to the current.
2. Description of the Related Art
A magnetic detection principle of a Hall element is described with reference to FIG. 4.
When current is passed through a semiconductor Hall element (Hall plate) in the shape of a rectangular parallelepiped having a length L, a width W, and a thickness d as illustrated in FIG. 4 in a direction of the length L and a magnetic field is applied perpendicularly to the flowing current, that is, in a direction of the thickness d, carriers that are electrons or holes flowing as the current are deflected by the Lorentz force in a direction perpendicular both to the applied magnetic field and to a travelling direction of the carriers, increasing the carriers at one end (accumulation) and reducing the carriers at another end in a direction of the width W. Accordingly, charge accumulates at the one end in the direction W that is perpendicular both to the direction of the current and to the direction of the magnetic field, and an electric field is generated along the direction W. Voltage generated by the electric field is called Hall voltage.
The generated Hall voltage VH is represented as:VH=(RHIB/d)cos θ,RH=1/(qn), orVH=μ(W/L)VinB cos θ,where Vin is a voltage applied by a power supply for passing a current I through the magnetic sensing portion, B is a density of a magnetic flux applied to the Hall element, e is an angle formed by a normal to the surface of the Hall element and the applied magnetic field, RH is the Hall coefficient, q is the charge of the carriers, n is a carrier concentration, and p is a carrier drift mobility. A ratio of the Hall voltage to the density of the applied magnetic flux is called sensitivity. It can be seen that, from the above expressions, in order to enhance the sensitivity per unit Hall current (so-called product sensitivity), it is effective to reduce d of the Hall plate or to reduce the carrier concentration. Further, in order to enhance the sensitivity per unit Vin, it is effective to increase W/L or to increase the mobility.
Potential distribution in the Hall element in the shape of such a rectangular parallelepiped is now reviewed. As described in R. S. Popovic “HALL EFFECT DEVICES, 2nd Edition” 2003, due to the Hall effect, charge accumulates at the one end of the magnetic sensing portion in the direction W, and an equipotential surface bends from a direction in parallel with current supply ends. It can be seen that the extent of the bend becomes larger as the distance from the current supply ends becomes larger, and thus, the largest Hall voltage is obtained when the voltage output is taken at about the center of the magnetic sensing portion in the direction L.
As a typical Hall element, a Hall element described in, for example, Kazusuke Maenaka, et al. “Integrated Three-Dimensional Magnetic Sensors” Trans. IEE Jpn. 109-C (1989), vol. 7, pp. 483-490, that is, a so-called horizontal Hall element, is known. The horizontal Hall element detects a magnetic field component perpendicular to a substrate surface.
FIG. 5A and FIG. 5B are illustrations of a typical horizontal Hall element. FIG. 5A is a plan view of the element, and FIG. 5B is a sectional view taken along the line L1-L1 of FIG. 5A. In the structure, for example, an n-type epitaxial layer 104, a well, or the like serving as a magnetic sensing portion is formed on a p-type substrate 103, and electrodes 105 that are heavily doped impurity regions are formed in four corners on a surface of the substrate. Current is passed between electrodes 105 in a pair formed on a diagonal line. At this time, current flows through the magnetic sensing portion in a direction in parallel with the substrate surface. The current generates the Hall voltage corresponding to the magnetic field in a direction perpendicular to the substrate surface. Through detection of the Hall voltage generated between electrodes in another pair formed on another diagonal line orthogonal to the diagonal line, the strength of the applied magnetic field can be determined.
In recent years, in addition to the horizontal Hall element, there is a vertical Hall element configured to detect a magnetic field in a direction in parallel with the substrate surface. In the case of the vertical Hall element, as described in Kazusuke Maenaka, et al. “Integrated Three-Dimensional Magnetic Sensors” Trans. IEE Jpn. 109-C (1989), vol. 7, pp. 483-490, by passing, through the magnetic sensing portion, current containing a component in the direction perpendicular to the substrate surface, the magnetic field in parallel with the substrate surface can be detected. The operating principles of the vertical Hall element and the horizontal Hall element are different only in the directions of the current and the magnetic field with respect to the substrate surface, and the principle of generating the Hall voltage is the same.
FIG. 6A to FIG. 6C are illustrations of a typical vertical Hall element. FIG. 6A is a plan view of the element, FIG. 6B is a sectional view taken along the line L1-L1 of FIG. 6A, and FIG. 6C is a sectional view taken along the line L2-L2 of FIG. 6A. On the substrate 103 of the first conductivity type, the epitaxial layer 104 of a second conductivity type opposite to that of the substrate is formed. A buried layer 106 that is a heavily doped impurity region of the second conductivity type that is the same as that of the epitaxial layer 104 is formed at the bottom of the epitaxial layer 104. Current supply ends 11 to 13 and voltage output ends 14 and 15 are both formed as heavily doped impurity regions. When voltage is applied between the current supply end 12 and the current supply ends 11 and 13, current flows between the current supply end 12 and the current supply ends 11 and 13 via the buried layer 106, and thus, current flowing between the current supply end 12 and the buried layer 106 perpendicularly to the substrate surface is obtained. As illustrated in FIG. 6A, the voltage output ends 14 and 15 are formed so as to be symmetrical with respect to the current supply end 12, and thus, when a magnetic field containing a component in parallel with the substrate surface is applied to the current, due to the Hall effect described above, the Hall voltage corresponding to the magnetic field is generated between the voltage output end 14 and the voltage output end 15. Therefore, through detection of voltage generated between the voltage output ends 14 and 15, the component of the applied magnetic field in the direction in parallel with the substrate surface can be determined.
Note that, the Hall plate illustrated in FIG. 4 in the shape of a rectangular parallelepiped in which the current density is constant throughout the element is only ideal, and does not establish itself in an actual horizontal or vertical Hall element. In the case of the vertical Hall element illustrated in FIG. 6A to FIG. 6C, the current density is concentrated immediately below the center current supply end 12 in the direction perpendicular to the substrate surface, and, as the distance from the electrode at the center increases, the current density sharply reduces. In a region in which the extent of the reduction is large, that is, around the current supply end 12 at the center, outflow/inflow difference of the carriers due to the Lorentz force is large, and thus, more charge is thought to accumulate. It follows that, through detection of the voltage in this region, the sensitivity is expected to be enhanced.
However, in a vertical Hall element configured to detect a magnetic field in a direction in parallel with the substrate surface based on current in a direction perpendicular to the substrate surface, a flow of current into a voltage output end for detecting the Hall voltage leads to a loss in obtaining current perpendicular to the substrate surface, and reduces the sensitivity. Therefore, it is important to restrict a flow of current into a voltage output end as much as possible, and measures such as forming voltage output ends away from current supply ends have been hitherto taken. However, this method leads to an increase in chip area. Further, increasing w/L in order to enhance the sensitivity per Vin also leads to an increase in chip area.